The US State Department sanctioned Kotey in January 2017, saying he was a guard for the “Beatles” and “likely engaged in the group’s executions and exceptionally cruel torture methods, including electronic shock and waterboarding.”

Kotey had also acted as a recruiter and was responsible for recruiting several British nationals to join the militant group, reports Reuters.

In March 2017, the State Department sanctioned Elsheikh, saying he was “said to have earned a reputation for waterboarding, mock executions, and crucifixions while serving as an ISIS jailer.”

The most notorious of the four was Mohammed Emwazi, known as “Jihadi John,” an executioner of hostages made famous by Islamic State videos of beheadings.

A US-British missile strike believed to have killed Emwazi, a British citizen of Arab origin, was months in preparation but came together at lightning speed in 2015 in the Syrian town of Raqqa, according to U.S. officials.

Emwazi became the public face of Islamic State and a symbol of its brutality after appearing in videos showing the murders of U.S. journalists Steven Sotloff and James Foley, U.S. aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto and other hostages.